Chromium overlays not properly mapped

The FlashControl Chromium plugin opens a tool overlay when clicking on its icon on the left of its URL bar. First screenshot shows it does not appear properly, only the left of the overlay is drawn. The second screenshot was not cropped, which means (by Gimp screenshot options) that this overlay is in fact in its own window. This one was made by moving the pointer, which unveiled buttons while flying over their intended space.